Post-translational processing of synaptophysin in the rat retina is disrupted by
Authors D'Cruz TS, Weibley BN, Kimball SR, Barber AJ
Submitted By Alistair Barber on 3/17/2014
Status Published
Journal PLoS ONE
Year 2012
Date Published
Volume : Pages 7 : e44711
PubMed Reference 22970294
Abstract Synaptophysin, is an abundant presynaptic protein involved in synaptic vesicle
recycling and neurotransmitter release. Previous work shows that its content is
significantly reduced in the rat retina by streptozotocin (STZ)-diabetes. This
study tested the hypothesis that STZ-diabetes alters synaptophysin protein
turnover and glycosylation in the rat retina. Whole explant retinas from male
Sprague-Dawley rats were used in this study. Rats were made diabetic by a single
intraperitoneal STZ injection (65 mg/kg body weight in 10 mM sodium citrate, pH
4.5). mRNA translation was measured using a (35)S-methionine labeling assay
followed by synaptophysin immunoprecipitation and autoradiography. A pulse-chase
study was used to determine the depletion of newly synthesized synaptophysin.
Depletion of total synaptophysin was determined after treatment with
cycloheximide. Mannose rich N-glycosylated synaptophysin was detected by
treating retinal lysates with endoglycosidase H followed by immunoblot analysis.
Synaptophysin mRNA translation was significantly increased after 1 month
(p<0.001) and 2 months (p<0.05) of STZ-diabetes, compared to age-matched
controls. Newly synthesized synaptophysin degradation was significantly
accelerated in the retina after 1 and 2 months of diabetes compared to controls
(p<0.05). Mannose rich glycosylated synaptophysin was significantly increased
after 1 month of STZ-diabetes compared to controls (p<0.05).These data suggest
that diabetes increases mRNA translation of synaptophysin in the retina,
resulting in an accumulation of mannose rich glycosylated synaptophysin, a
transient post-translational state of the protein. This diabetes-induced
irregularity in post-translational processing could explain the accelerated
degradation of retinal synaptophysin in diabetes.

Investigators with authorship
Alistair BarberPennsylvania State University-Penn State College of Medicine